Extrusion die head with reversed-flow and adjustable-choke structure

ABSTRACT

A die head especially suitable in producing blown film and pipe wherein the parts are internally shaped to define a circular manifold chamber resulting from annular tongue-and-groove structure whereby a short axial reversal in the generally forward flow of material through the die head may be effected. The die head, in a preferred form, contains an axially adjustable choke ring within the groove of the tongue-and-groove structure for varying back pressure on the material supplied to the die head.

ilite Kovacs [54] EXTRUSION DIE HEAD WITH [15] 3,690,806 51 Sept. 12,1972 3,090,995 5/1963 Amsden ..18/5 BE X REVERSED-FLOW AND ADJUSTABLE-2,688,154 9/1954 Huckfeldt ..18/14 G CHOKE STRUCTURE 3,418,685 12/1968Anderson et a] ..18/12 N 2,978,748 4/1961 McCauley et a] ..425/380 [72]Kmcs Smerset' 3,307,217 3/1967 Cameron ..425/376 x [73] Assignee:Midland-Ross Corporation,

' Cleveland. Ohio Primary Examiner-J. Spencer Overholser [22] Filed: 0c.15, 1970 Assistant Examiner-David S. Safran Attorney-Woodrow W. Portzand Irvin L. Groh [21] Appl. No.: 80,977

. [57] ABSTRACT [52] US. Cl ..425/467, 425/380 A die head especiallysuitable i producing blown film [51] Int. Cl. ..B29f 3/01 and pipewherein the parts are internally shaped to [58] Flew of Search "18/12 3030 14 define a circular manifold chamber resulting from an- 18/14 G, 12DM, 12 N, 14 P, 14 RR, 14 V, nular tongue-and-groove structure whereby ashort 425/376 467 axial reversal in the generally forward flow ofmaterial through the die head may be effected. The die head, [56]Regerences Cited in a preferred form, contains an axially adjustableUNITED STATES PATENTS choke ring within the groove of thetongue-and-grooye structure for varying back pressure on the material3,546,743 12/1970 Roth ..18/14 P Supplied to the die heacL 3,010,15411/1961 Swenson ..l8/30JTX 2,405,039 7/1946 Jesionowski ..18/12 DM 4Claims, 3 Drawing Figures 1 F3 /J 3/ i ,i I I I 2442 52" 45 52 1! i? e4% r f H z/zz *7 37 5 Z4 M /Z l &7 1 Z a? Patented Sept. 12, 1972INVENTOR. LLUVD KOVflCS #TTSKIWFV 5 TQFm BACKGROUND In obtainingsatisfactory extrusion of thin-walled tubes or parisons from die heads,extreme uniformity of temperature, texture, and rate of flow isessential in order to obtain product, such as film, which is free ofdefects as it leaves the discharge orifice of the die. In making thepresent invention, it is recognized that slight complex variations inthe flow of molten plastic through a tube-forming die, especially afilm-forming die, cause obvious defects in the film. It is recognizedheretofore that some restriction in the passage of melt causing backpressure, particularly in the less advanced spaces in the flow route ofthe melt within the die, is desirable for avoiding variations intemperature, texture, and flow.

- In making this invention, it is further recognized that there aredifferences in the behavoir of various thermoplastic resins atrespective optimum extruding temperatures which cause an interior dieconfiguration which issuitable for one resin to be unsuitable foranother.

Hence, it is an important object of this invention to provide a tube orfilm-blowing die head of compact design which is capable of dischargingan exceedingly homogeneous product in blemish-free condition and atuniform thickness.

Another object is to provide die heads having internalmaterial-forwarding manifolds in accordance with the foregoing object inwhich structure for feeding the manifolds may be arranged for passage ofsupply melt along the center of a die or through the side of the die.

A further object is to provide a die having adjustable structure forvarying the restriction to the passage of melt through the die head toobtain satisfactory product under conditions of varying temperature,viscosity, and swelling characteristics as the product issues from thedie.

' The die head has, in a conventional sense, a body member having alongitudinal axis and an inner surface defining a transversely circularlongitudinally-extending opening centered along the axis, an adaptermember by which the die head is secured to an extruder or other sourcefor melted plastic and providing an inlet passageway for the die head,and a mandrel member which extends generally coaxially within the bodymember to form an annular region therebetween through which the meltpasses longitudinally through the die head and between tube-forming diesurfaces.

BRIEF SUMMARY The present invention resides in the shaping of theabove-described members in such a manner as to define anaxially-extending annular tongue, and a groove in one or two of themembers which receives the tongue in spaced relation withgroove-defining surfaces. The tongue-and-groove structure thus providesa flow route in which material undergoes reversal of axial directionwhile moving in a generally radial direction into an annularfluid-conducting region between the inner surface of the body member andthe outer surface of the mandrel member. In the preferred embodiment,the groove is formed with sufficient depth as to house a choke ringwhich may be traversed in an axial direction within the groove by anadjusting means capable of fixedly supporting the choke ring in variouspositions. By such change of position, the distance of the ring from theend surface of the tongue may be adjusted to vary the capacity of theflow route for melted material around the end of the tongue, and tocreate a suitable back pressure upstream from the tongue. By using thechoke ring to constrict the flow route, the back pressure may be raisedwith corresponding changes in the linear rate of flow and amount ofmaterial passing I around the end of the tongue. With experience,adjustment of the choke ring is made in accordance with any particularset of operating conditions adopted and in view of differences in thephysical and chemical nature of a thermoplastic resin to be passedthrough the die head equipment to attain desired extrusion quality.

FIGURES OF THE DRAWING In the drawing with respect to which theinvention is described:

FIG. 1 is a longitudinal section along a diametral plane of a die headin accordance with one embodiment of the invention;

FIG. 2 is a diametral section taken along line Il--Il of FIG. 1;

FIG. 3 is a bottom end view of the die head of FIG. 1;

The drawing illustrates an relate to a first-described embodiment inwhich an extrusion die head 4 comprises, as its major parts, an adapter5, a generally cylindrical body member 6 attached to the adapter, amandrel 7 attached to the adapter, detachable and replaceable parison ortube-forming elements comprising an annular head ring 8 attached to'thebody 6 and a mandrel tip 9 attached to the mandrel 7. The extrusion headfurther includes a retainer ring 10 which engages a front-facing surfaceof the head ring 8 and is held approximately against the front end ofthe body 6 by means, such as cap screws 12.

DETAILED DESCRIPTION The adapter 5 is a portion of the extrusion head bywhich the head is attached to a supply source for extrudate, such as ascrew extruder or injection cylinder not shown. Junction with such asource is made along a flat laterally-facing surface 15 with a dischargeduct of the supply device in alignment with a radially-extending port 16opening in the surface 15. The port 16 joins with an axial bore 18 whichextends in lengthwise concentric relation with the axis of the head intoa manifold region comprising radial channels 19 extending to the outersurface of the adapter 5 from the front or fluid-discharging end of thebore. The adapter 5 is constructed with a longitudinal projectionincluding a cylindrically-shaped exteriorly-threaded boss 21 received ina complementary interiorlythreaded recess 22 of the mandrel 7. Thefrontwardly-projecting portion of the adapter also contains the channels19 the outer ends of which are contiguous with the primary circularregion enclosed by the body 6.

To complete the manifold region consisting in part of the channels 19,the mandrel 7 has an annular tongue 24 in concentric relation with theprojecting portion of the adapter and in sufficiently spaced relationwith the radially-outer ends of the channels 19 to define a circularspace 25 contiguous with all channels 19 to complete the above-mentionedmanifold region. The tongue 24 is also in inward radially-spacedrelation with the inner surface 26 of the body 6 and a radiallyinwardly-facing surface 27 of the adapter which partially form a deepannular recess 28 for receiving a choke ring 30.

As FIGS. 1 and 3 show, the choke ring 30 is supported in a precise axialposition by two sets of cap screws extending through the adapter in anaxial direction along a single circumference or circle. One set of capscrews 31 have their heads in seated relation with a shoulder formed bya counterbore in the adapter, in threaded adjustable relation with thechoke ring. The other set of cap screws 32 are in threaded relation withthe adapter but in compressive engaging relation with the rear surfaceof the choke ring. By adjustment of the two sets of cap screws, thechoke ring may be adjusted and fixed in position at any distance fromthe tongue 24 permitted by the depth of the recess 28 to establish a gapor a clearance between the tongue and the choke ring.

As the adapter is secured in sealed relation with the body 6 by aplurality of cap screws 34, a flow path is now defined through the headcommencing with the port 16 and continuing through the bore 18, channels19, the circular space 25, the circular gap 32, and a region between theouter surface of the mandrel 7 and the inner surface of the body 6contiguous with the gap 32. The flow path terminates in the annulardischarge orifice 34 of the head and is completed by the annularclearance between the mandrel tip 9 and the head ring 8. The latterelements are normally replaceable to obtain orifices of different sizeswith corresponding product tubes of different thicknesses and diameters.The extrusion head, as illustrated in FIGS. 1, 2 and 3, has attached tovarious outer surfaces thereof electrical strip heaters 35, 36 and 37.

As the extrusion head of FIGS. 1-3 is of the filmblowing type, passageof air for the head from a supply tube 39 is provided by way of alateral duct 41, an axial duct 39 joining therewith within the adapterand terminating at the end of the boss 21 in an end clearance 42. Theduct 39 communicates through the end clearance with an axially-centeredduct 43 and an axially-centered duct 44 of the head mandrel connected inthreaded relationship with the mandrel 7.

lclaim:

1. An extrusion die head comprising:

a body member having a longitudinal axis and an inner surface defining atransversely circular iontending, annular and concer itric flali-conducting tongue-and-groove means ocate etween and connecting thepassageway and said region and having all portions of the tongue meansin spaced relation with the groove means to provide at least oneinstance of axial reversal in the flow of fluid from said passageway tosaid region;

a choke ring received in said groove means in opposed relation with theend surface of the tongue means, said groove means being of sufficientdepth permitting movement of the ring toward and away from said endsurface;

adjustable means carried by said adapter member for moving said ring inan axial direction toward and away from said end surface.

2. The die head of claim 1 wherein:

said groove means includes a groove in the adapter of such depth in anaxial direction as to substantially and completely accommodate the chokering.

3. The die head of claim 1 comprising:

one set of puller-type cap screws supported with the heads thereofseated on said adapter member and end portions in threaded adjustablerelation with said choke ring, and another set of pusher-type cap screwsin threaded relation with the adapter member with the ends thereof inengaging relation with the end surface of said choke ring in opposedrelation with said tongue means, all said cap screws extending ingenerally parallel relation with said passageway.

4. The die head of claim 3 wherein:

both sets of cap screws are arranged along a single circumferencecentered about said longitudinal axis.

1. An extrusion die head comprising: a body member having a longitudinalaxis and an inner surface defining a transversely circularlongitudinally-extending opening centered along said axis; an adaptermember secured to said body and having an inlet passageway, said adapterclosing one end of the opening except for communication thereof withsaid passageway; a mandrel member received in said opening and means forlocating said mandrel member in fixed coaxial relation with said othermembers, said mandrel member being radially spaced from the innersurface to define an annular region for passage of a fluid lengthwise ofsaid axis to outwardly of said die head; and said members havingportions defining axially-extending, annular and concentricfluid-conducting, tongue-and-groove means located between and connectingthe passageway and said region and having all portions of the tonguemeans in spaced relation with the groove means to provide at least oneinstance of axial reversal in the flow of fluid from said passageway tosaid region; a choke ring received in said groove means in opposedrelation with the end surface of the tongue means, said groove meansbeing of sufficient depth permitting movement of the ring toward andaway from said end surface; adjustable means carried by said adaptermember for moving said ring in an axial direction toward and away fromsaid end surface.
 2. The die head of claim 1 wherein: said groove meansincludes a groove in the adapter of such depth in an axial direction asto substantially and completely accommodate the choke ring.
 3. The diehead of claim 1 comprising: one set of puller-type cap screws supportedwith the heads thereof seated on said adapter member and end portions inthreaded adjustable relation with said choke ring, and another set ofpusher-type cap screws in threaded relation with the adapter member withthe ends thereof in engaging relation with the end surface of said chokering in opposed relation with said tongue means, all said cap screwsextending in generally parallel relation with said passageway.
 4. Thedie head of claim 3 wherein: both sets of cap screws are arranged alonga single circumference centered about said longitudinal axis.